title: miR-34a induces the downregulation of both E2F1 and B-Myb oncogenes in leukemic cells.
abstract: OBJECTIVE
  To elucidate new molecular mechanisms able to downregulate the mRNA levels of key oncogenes, such as B-Myb and E2F1, in a therapeutic perspective.
  
  
  METHODS
  B-Myb and E2F1 mRNA levels were evaluated in primary B chronic lymphocytic leukemia (B-CLL, n = 10) and acute myeloid leukemia (AML, n = 5) patient cells, in a variety of p53(wild-type) and p53(mutated/deleted) leukemic cell lines, as well as in primary endothelial cells and fibroblasts. Knockdown experiments with siRNA for p53 and E2F1 and overexpression experiments with miR34a were conducted to elucidate the role of these pathways in promoting B-Myb downregulation.
  
  
  RESULTS
  In vitro exposure to Nutlin-3, a nongenotoxic activator of p53, variably downregulated the expression of B-Myb in primary leukemic cells and in p53(wild-type) myeloid (OCI, MOLM) and lymphoblastoid (SKW6.4, EHEB) but not in p53(mutated) (NB4, BJAB, MAVER) or p53(deleted) (HL-60) leukemic cell lines. The transcriptional repression of B-Myb was also observed in primary normal endothelial cells and fibroblasts. B-Myb downregulation played a critical role in the cell-cycle block in G(1) phase induced by Nutlin-3, as shown by transfection experiments with specific siRNA. Moreover, we have provided experimental evidence suggesting that miR-34a is a central mediator in the repression of B-Myb both directly and through E2F1.
  
  
  CONCLUSIONS
  Owing to the role of B-Myb and E2F1 transcription factors in controlling cell-cycle progression of leukemic cells, the downregulation of these oncogenes by miR-34a suggests the usefulness of therapeutic approaches aimed to modulate the levels of miR-34a.
authors.affiliation: Institute for Maternal and Child Health, IRCCS Burlo Garofolo, Trieste, Italy.
authors.forename: Giorgio
authors.initials: G
authors.lastname: Zauli
authors.forename: Rebecca
authors.initials: R
authors.lastname: Voltan
authors.forename: Maria Grazia
authors.initials: MG
authors.lastname: di Iasio
authors.forename: Raffaella
authors.initials: R
authors.lastname: Bosco
authors.forename: Elisabetta
authors.initials: E
authors.lastname: Melloni
authors.forename: Maria Elena
authors.initials: ME
authors.lastname: Sana
authors.forename: Paola
authors.initials: P
authors.lastname: Secchiero
mesh_terms: D001483:Base Sequence; D018797:Cell Cycle Proteins / Q000235:genetics* / Q000378:metabolism; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D015536:Down-Regulation / Q000187:drug effects / Q000235:genetics; D050687:E2F1 Transcription Factor / Q000235:genetics* / Q000378:metabolism; D015973:Gene Expression Regulation, Leukemic / Q000187:drug effects / Q000235:genetics; D045325:HCT116 Cells; D018922:HL-60 Cells; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D007938:Leukemia / Q000235:genetics* / Q000473:pathology; D035683:MicroRNAs / Q000235:genetics / Q000502:physiology*; D008954:Models, Biological; D009857:Oncogenes / Q000235:genetics; D010879:Piperazines / Q000494:pharmacology; D012689:Sequence Homology, Nucleic Acid; D015534:Trans-Activators / Q000235:genetics* / Q000378:metabolism; D014162:Transfection
chemical_list: D018797:Cell Cycle Proteins; D050687:E2F1 Transcription Factor; D007093:Imidazoles; C522425:MIRN34 microRNA, human; C064352:MYBL2 protein, human; D035683:MicroRNAs; D010879:Piperazines; D015534:Trans-Activators; C482205:nutlin 3